Methods for driving bistable electro-optic displays, and apparatus for use therein

Abstract

A bistable electro-optic display has a plurality of pixels, each of which is capable of displaying at least three gray levels. The display is driven by a method comprising: storing a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level; storing data representing at least an initial state of each pixel of the display; receiving an input signal representing a desired final state of at least one pixel of the display; and generating an output signal representing the impulse necessary to convert the initial state of said one pixel to the desired final state thereof, as determined from said look-up table. The invention also provides a method for reducing the remnant voltage of an electro-optic display.

What is claimed is:  
     
       1. A method of driving a bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, the method comprising:
 storing a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level;  
 storing data representing at least an initial state of each pixel of the display;  
 storing data representing at least one prior state of each pixel prior to said initial state thereof,  
 receiving an input signal representing a desired final state of at least one pixel of the display; and  
 generating an output signal representing the impulse necessary to convert the initial state of said one pixel to the desired final state thereof, as determined from said look-up table, wherein said output signal is generated dependent upon both said at least one prior state and said initial state of said one pixel.  
 
     
     
       2. A method according to  claim 1  wherein data is stored representing at least two prior states of each pixel and said output signal is generated dependent upon said at least two prior states and said initial state of said one pixel. 
     
     
       3. A method according to  claim 1  further comprising receiving a temperature signal representing the temperature of at least one pixel of the display and generating said output signal dependent upon said temperature signal. 
     
     
       4. A method according to  claim 3  wherein said look-up table stores multiple values for each transition from an initial gray level to a final gray level, said multiple values representing the values required for a specific transition at a specific temperature. 
     
     
       5. A method according to  claim 4  further comprising interpolating between adjacent values for a transition when the temperature signal indicates a temperature intermediate the temperatures to which said adjacent values relate. 
     
     
       6. A method according to  claim 3  wherein said look-up table stores functions of temperature, and wherein said output signal is generated by calculating the value of the relevant function at the temperature indicated by said temperature signal. 
     
     
       7. A method according to  claim 1  wherein said output signal represents the period of time for which a substantially constant drive voltage is to be applied to said pixel. 
     
     
       8. A method according to  claim 7  wherein said pixel is driven in a scan comprising a plurality of sub-scan periods and said output signal determines during which of said sub-scan periods a drive voltage is to be applied to said pixel. 
     
     
       9. A method according to  claim 1  wherein said output signal comprises at least one polarity bit representing the polarity of the impulse necessary to convert the initial state of said one pixel to the desired final state thereof. 
     
     
       10. A method according to  claim 1  wherein there is applied to said one pixel in succession a pre-pulse which drives said one pixel to one of its extreme optical states, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       11. A method according to  claim 10  wherein the pixels of the display are divided into first and second groups and different pre-pulses are applied to the first and second groups so that the pre-pulse drives the first group of pixels to one extreme optical state and the second group of pixels to the opposed extreme optical state. 
     
     
       12. A method according to  claim 1  wherein there is applied to said one pixel in succession a first pre-pulse which drives said one pixel to one of its extreme optical states, a second pre-pulse which drives said one pixel from said one extreme optical state to the opposed extreme optical state, and an addressing pulse which drives said one pixel from said opposed extreme optical state to the desired final state. 
     
     
       13. A method according to  claim 1  wherein the display is an electrophoretic display. 
     
     
       14. A method according to  claim 13  wherein the display is an encapsulated electrophoretic display. 
     
     
       15. A method according to  claim 1  wherein the display is a microcell display comprising charged particles and a suspending fluid retained within a plurality of cavities formed in a carrier medium. 
     
     
       16. A method according to  claim 1  wherein the display is a passive matrix display. 
     
     
       17. A method of driving a bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, the method comprising:
 storing a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level;  
 storing data representing at least an initial state of each pixel of the display;  
 receiving an input signal representing a desired final state of at least one pixel of the display;  
 generating a lifetime signal representing the operating time of said one pixel; and  
 generating an output signal representing the impulse necessary to convert the initial state of said one pixel to the desired final state thereof, as determined from said look-up table, said output signal being generated dependent upon said lifetime signal.  
 
     
     
       18. A method according to  claim 17  wherein there is applied to said one pixel in succession a pre-pulse which drives said one pixel to one of its extreme optical states, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       19. A method according to  claim 18  wherein the pixels of the display are divided into first and second groups and different pre-pulses are applied to the first and second groups so that the pre-pulse drives the first group of pixels to one extreme optical state and the second group of pixels to the opposed extreme optical state. 
     
     
       20. A method according to  claim 17  wherein there is applied to said one pixel in succession a first pre-pulse which drives said one pixel to one of its extreme optical states, a second pre-pulse which drives said one pixel from said one extreme optical state to the opposed extreme optical state, and an addressing pulse which drives said one pixel from said opposed extreme optical state to the desired final state. 
     
     
       21. A method according to  claim 17  wherein the display is an electrophoretic display. 
     
     
       22. A method according to  claim 21  wherein the display is an encapsulated electrophoretic display. 
     
     
       23. A method according to  claim 17  wherein the display is a microcell display comprising charged particles and a suspending fluid retained within a plurality of cavities formed in a carrier medium. 
     
     
       24. A method according to  claim 17  wherein the display is a passive matrix display. 
     
     
       25. A method of driving a bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, the method comprising:
 storing a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level;  
 storing data representing at least an initial state of each pixel of the display;  
 receiving an input signal representing a desired final state of at least one pixel of the display;  
 generating a residence time signal representing the time since said one pixel underwent a transition; and  
 generating an output signal representing the impulse necessary to convert the initial state of said one pixel to the desired final state thereof, as determined from said look-up table, said output signal being generated dependent upon said residence time signal.  
 
     
     
       26. A method according to  claim 25  wherein there is applied to said one pixel in succession a pre-pulse which drives said one pixel to one of its extreme optical states, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       27. A method according to  claim 26  wherein the pixels of the display are divided into first and second groups and different pre-pulses are applied to the first and second groups so that the pre-pulse drives the first group of pixels to one extreme optical state and the second group of pixels to the opposed extreme optical state. 
     
     
       28. A method according to  claim 25  wherein there is applied to said one pixel in succession a first pre-pulse which drives said one pixel to one of its extreme optical states, a second pre-pulse which drives said one pixel from said one extreme optical state to the opposed extreme optical state, and an addressing pulse which drives said one pixel from said opposed extreme optical state to the desired final state. 
     
     
       29. A method according to  claim 25  wherein the display is an electrophoretic display. 
     
     
       30. A method according to  claim 29  wherein the display is an encapsulated electrophoretic display. 
     
     
       31. A method according to  claim 25  wherein the display is a microcell display comprising charged particles and a suspending fluid retained within a plurality of cavities formed in a carrier medium. 
     
     
       32. A method according to  claim 25  wherein the display is a passive matrix display. 
     
     
       33. A device controller for controlling a bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, said controller comprising:
 storage means arranged to store both a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level, and data representing at least an initial state of each pixel of the display, said storage means also being arranged to store data representing a least one prior state of each pixel prior to said initial state thereof;  
 input means for receiving an input signal representing a desired final state of at least one pixel of the display;  
 calculation means for determining, from the input signal, the stored data representing the initial and prior states of said pixel, and the look-up table, the impulse required to change the initial state of said one pixel to the desired final state; and  
 output means for generating an output signal representative of said impulse.  
 
     
     
       34. A controller according to  claim 33  wherein said storage means is arranged to store data representing at least two prior states of each pixel, and said calculation means is arranged to determine said impulse dependent upon said input signal, said initial state of said pixel and said at least two prior states of said pixel. 
     
     
       35. A controller according to  claim 33  wherein said output means generates a signal representing the time for which a substantially constant drive voltage is to be applied to said pixel. 
     
     
       36. A controller according to  claim 33  wherein said output signal comprises at least one polarity bit representing the polarity of said impulse. 
     
     
       37. A controller according to  claim 33  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       38. A controller according to  claim 33  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, a second pre-pulse which drives said one pixel from said one extreme optical state to the opposed extreme optical state, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       39. A bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, and a controller according to  claim 33  arranged to control the electro-optic display. 
     
     
       40. A device controller for controlling a bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, said controller comprising:
 storage means arranged to store both a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level, and data representing at least an initial state of each pixel of the display,  
 input means for receiving an input signal representing a desired final state of at least one pixel of the display, said input means also being arranged to receive a temperature signal representing the temperature of at least one pixel of the display;  
 calculation means for determining, from the input signal, the stored data representing the initial state of said pixel, said temperature signal, and the look-up table, the impulse required to change the initial state of said one pixel to the desired final state; and  
 output means for generating an output signal representative of said impulse.  
 
     
     
       41. A controller according to  claim 40  wherein said storage means is arranged to store multiple values for the impulses necessary to convert an initial gray level to a final gray level, said multiple values representing the values required for a specific transition at a specific temperature. 
     
     
       42. A controller according to  claim 41  wherein said calculation means is arranged to interpolate between adjacent ones of said stored multiple values when said temperature signal indicates a temperature intermediate the temperatures to which said adjacent stored values relate. 
     
     
       43. A controller according to  claim 40  wherein said storage means is arranged to store functions of temperature, and said calculation means is arranged to determine said impulse by calculating the value of the relevant function at the temperature represented by said temperature signal. 
     
     
       44. A controller according to  claim 40  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       45. A controller according to  claim 40  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, a second pre-pulse which drives said one pixel from said one extreme optical state to the opposed extreme optical state, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       46. A bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, and a controller according to  claim 40  arranged to control the electro-optic display. 
     
     
       47. A device controller for controlling a bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, said controller comprising:
 storage means arranged to store both a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level, and data representing at least an initial state of each pixel of the display,  
 input means for receiving an input signal representing a desired final state of at least one pixel of the display;  
 lifetime signal generation means arranged to generate a lifetime signal representing the operating time of said pixel  
 calculation means for determining, from the input signal, the stored data representing the initial state of said pixel, said lifetime signal, and the look-up table, the impulse required to change the initial state of said one pixel to the desired final state; and  
 output means for generating an output signal representative of said impulse.  
 
     
     
       48. A controller according to  claim 42  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       49. A controller according to  claim 42  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, a second pre-pulse which drives said one pixel from said one extreme optical state to the opposed extreme optical state, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       50. A bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, and a controller according to  claim 47  arranged to control the electro-optic display. 
     
     
       51. A device controller for controlling a bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, said controller comprising:
 storage means arranged to store both a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level, and data representing at least an initial state of each pixel of the display,  
 input means for receiving an input signal representing a desired final state of at least one pixel of the display;  
 residence time signal generation means for determining the residence time since said one pixel last underwent a transition and for generating a residence time signal representing said residence time;  
 calculation means for determining, from the input signal, the stored data representing the initial state of said pixel, said residence time signal, and the look-up table, the impulse required to change the initial state of said one pixel to the desired final state; and  
 output means for generating an output signal representative of said impulse.  
 
     
     
       52. A controller according to  claim 51  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       53. A controller according to  claim 51  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, a second pre-pulse which drives said one pixel from said one extreme optical state to the opposed extreme optical state, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       54. A bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, and a controller according to  claim 51  arranged to control the electro-optic display. 
     
     
       55. A device controller comprising:
 storage means arranged to store both a look-up table containing data representing the impulses necessary to convert an initial gray level to a final gray level, and data representing at least an initial state of each pixel of the display;  
 input means for receiving an input signal representing a desired final state of at least one pixel of the display;  
 calculation means for determining, from the input signal, the stored data representing the initial state of said pixel, and the look-up table, the impulse required to change the initial state of said one pixel to the desired final state; and  
 output means for generating an output signal representative of said impulse, the output signal representing a plurality of pulses varying in at least one of voltage and duration, the output signal representing a zero voltage after the expiration of a predetermined period of time.  
 
     
     
       56. A controller according to  claim 55  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       57. A controller according to  claim 55  wherein said output means is arranged to generate in succession a pre-pulse which drives one pixel of its associated display to one of its extreme optical states, a second pre-pulse which drives said one pixel from said one extreme optical state to the opposed extreme optical state, and an addressing pulse which drives said one pixel from said one extreme optical state to the desired final state. 
     
     
       58. A bistable electro-optic display having a plurality of pixels, each of which is capable of displaying at least three gray levels, and a controller according to  claim 55  arranged to control the electro-optic display. 
     
     
       59. A driver circuit comprising:
 output lines arranged to be connected to drive electrodes of an electro-optic display;  
 first input means for receiving a plurality of 2-bit numbers representing the voltage and polarity of signals to be placed on the drive electrodes; and  
 second input means for receiving a clock signal,  
 the driver circuit being arranged such that, upon receipt of the clock signal, the driver circuit displays voltages selected from R+V, R and R−V on its output lines, where R is a reference voltage and V is the maximum difference from the reference voltage which the driver circuit can assert.  
 
     
     
       60. A method for driving an electro-optic display having a remnant voltage, the method comprising:
 (a) applying a first driving pulse to a pixel of the display;  
 (b) measuring the remnant voltage of the pixel after the first driving pulse; and  
 (c) applying a second driving pulse to the pixel following the measurement of the remnant voltage, the magnitude of the second driving pulse being controlled dependent upon the measured remnant voltage to reduce the remnant voltage of the pixel.  
 
     
     
       61. A method according to  claim 60  wherein the display is of the direct drive type having a plurality of pixels each of which is provided with a separate electrode, the display further comprising switching means arranged to control independently the voltage applied to each electrode. 
     
     
       62. A method according to  claim 60  wherein the display comprises a plurality of pixels and there is applied to the display at intervals a blanking pulse which drives all the pixels of the display to substantially the same display state, and measurement of the remnant voltage is effected after such a blanking pulse. 
     
     
       63. A method according to  claim 60  wherein the display is an electrophoretic display. 
     
     
       64. A method according to  claim 63  wherein the display is an encapsulated electrophoretic display. 
     
     
       65. A method according to  claim 60  wherein the display is a microcell display comprising charged particles and a suspending fluid retained within a plurality of cavities formed in a carrier medium. 
     
     
       66. A method according to  claim 60  wherein the display is a passive matrix display.